Avalanche Forecast
Issued: Jan 13th, 2018 10:13AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Loose Wet.
NWAC,
Northwest Avalanche Center
Winds slabs formed during the past week continue to linger near and above treeline. Avalanches are most likely to trigger in areas such as unsupported slopes, convex roles, and near shallow spots within the snowpack. Warm temperatures and mostly clear skies will create wet surface snow on sunny slopes. It only takes a few inches of wet surface snow to create and avalanche.
Summary
Detailed Forecast
Warm temperatures and mostly sunny skies will provide another day for lingering wind slabs to gain strength. While the likelihood of triggering these avalanches is decreasing it is still possible. Identify and avoid areas where avalanche are more likely to trigger such as unsupported slopes, convex rolls, and shallow spots within the snowpack.
Surface crust formed Saturday night will delay but not eliminate potential loose wet avalanches on Sunday. Warm temperatures and mostly clear skies will help break down the crust on sunny slopes. This is most likely to occur in rocky and shallow areas where surface warming is accelerated. Watch for changes in surface snow conditions as you travel. It only takes a few inches of wet surface snow to cause an avalanche.
Despite the recent snow, early season hazards still exist. Many creek beds have still not filled in for the winter.
Snowpack Discussion
Mild temperatures and afternoon sun breaks allowed the upper snowpack to gain strength on Saturday. Moist to wet snow was found at the surface near and below treeline due to warm temperatures and scattered rain showers. Clear skies Saturday night should allow surface snow to refreeze forming a surface crust on most slopes.
Last week’s storms brought 8-14 inches of snow to the east slopes of the Cascades. Winds throughout the storm periods redistributed snow, forming wind slabs on a variety of aspects especially in exposed terrain.
A supportive crust (1/5) formed from a widespread freezing rain event in the central-east zone, extending to the Stevens and Snoqualmie Pass areas. This layer is not present in the northeast from Washington Pass to Holden.
Snowdepth still decreases substantially east of the Cascade crest. In many areas below treeline, there has not been enough snow to present an avalanche danger.
Observations
North
North Cascades Heli was in the field Saturday and observed thin wind slabs, 8 inches thick on lee slopes. Roller balls were reported on sunny slopes in the afternoon, but natural loose wet avalanche was not observed.
Guides from both North Cascades Mountain Guides and North Cascades Heli were in the field Friday. Observations suggest storm snow weaknesses are gaining strength.
Central
Mission Ridge Pro Patrol Friday reported upside-down new storm snow. Avalanches observed failed within the storm snow.
Older but still relevant observations:
Several observations from the Mission Ridge and Blewett Pass areas have reported 2-3mm facets on the ground, including a recent post found here. This layer will need to be monitored. It could develop into a potentially dangerous weak layer in the future.
South
No recent observations
Problems
Wind Slabs
Release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Loose Wet
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Aspects: East, South East, South, South West, West.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Jan 14th, 2018 10:13AM
